Phase-shifting coronagraph

Transcription

1 Phase-shifting coronagraph François Hénault, Alexis Carlotti, Christophe Vérinaud Institut de Planétologie et d Astrophysique de Grenoble Université Grenoble-Alpes Centre National de la Recherche Scientifique BP 53, Grenoble France Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

2 Plan of presentation Goal of the study Principle Optical design Numerical model Simulation of measures intensities Wavefront reconstruction procedure Numerical simulations hree different phase-shifting schemes hree types of phase mask coronagraphs wo typical wavefront errors (to be measured) Interpretation of the results Conclusion Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

3 Goal of the study Evaluate the measurement accuracy of wavefront sensing phase-shifting methods from inside a coronagraph Put the phase-shifting device as far as possible within the coronagraph to compensate for Non common path aberrations (NCPA) Compare phase-shifting in the pupil with phaseshifting in the image Evaluate validity range: Limited to weak aberrations or only by 2π-ambiguity [-λ/2,+λ/2]? Real or low-order wavefront sensor? Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

4 A brief history of phase-shifting telescopes 1 Entrance Wave-front W ELESCOPE Secondary Primary Focal Plane MACH-ZEHNDER INERFEROMEER Spatial Filter Phase- Shifting Device Plane Plane 2 Entrance Wave-front W Auxiliary Optics ELESCOPE Secondary Single Mode Optical Fiber Primary α Focal Plane R. Angel, Nature (1994) F. Hénault, Applied Optics (2005) ELESCOPE Primary 3 ELESCOPE Primary Entrance Wave-front W Auxiliary Optics Secondary Cylinder PZ Focal Plane Entrance Wave-front W Secondary Focal Plane Plane Relay Optics ZERNIKE WAVEFRON SENSOR Phase- Shifting Device 4 Parabolic F. Hénault, Optics Communications (2006) J. K. Wallace et al, Proc. SPIE (2011) Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

5 Principle hree different phase-shifting schemes: Phase-shifting device Image mask Lyot stop O O O 1 - In telescope 1 2 pupil Coronagraphic O In Lyot stop - In coronagraph image LOWFS O O O 3 O L1 L2 L3 Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

6 Optical design Phase-shifting in /Lyot stop Sensing in image Phase-shifting in coronagraph image Sensing in pupil Phase- M 1 M 2 Phase- L 5 M 1 M 2 shift φ m shift φ m L1 Phase mask L2 Beam splitter Pick-off mirror M1 L1 Phase mask L2 Beam splitter L4 Pick-off mirror M1 Lyot stop L3 Combining mirror M3 L6 M2 Lyot stop L3 Detectors in pupil BS2 L5 M2 Coronagraph image Detector in image Coronagraph image Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

7 Numerical model Module 1: Complex amplitude propagation from to via Fourier transforms (see next slides) Module 2: Simplified WFE reconstruction procedure using two Dirac Delta approximations d D Phaseshifting area d Delta approximation in pupil d / D << 1 Delta approximation in image d < λf/d Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

8 Numerical simulations hree different types of phase mask coronagraphs Roddier π Four- Quadrant π 0 0 π Vortex wo typical wavefront errors PV λ RMS λ PV λ RMS λ Low spatial frequency WFE Mid spatial frequency WFE Input WFE Input WFE Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

9 Numerical simulations Phase-shifting in Lyot stop (four-quadrant phase mask) COMPLEX AMPLIUDE SIMULAIONS (FOURIER OPICS) MEASURED INENSIIES WFE RECONSRUCION PROCCESS Re [ A ( P )] Im[ A ( P )] 1 1 ( M 1 ) I F Re A ˆ ( M ) F -1 F 2 e iϕ F -1 Arg Re[ P ˆ( M )] Re[ iϕ Pˆ ( M ) ] Re[ P ( P )] e W ( P) Re [ A ( P )] Im[ A ( P )] 2 2 ( M 2 ) I W ( P ) Im [ A ˆ ( M )] Im [ P ˆ( M )] e iϕ Im [ Pˆ ( M ) ] Im [ P ( P )] Reconstructed WFE Image mask Re [ A ( P )] Im[ A ( P )] 3 3 ( M ) I 3 Phase-shift algorithm Phase mask multiplication Complex amplitude in pupil Lyot stop No Delta approximations here Coronagraphic WFE reconstruction based oh Delta approximation Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

10 Numerical simulations Phase-shifting in coronagraph image (vortex phase mask) COMPLEX AMPLIUDE SIMULAIONS (FOURIER OPICS) MEASURED INENSIIES WFE RECONSRUCION PROCCESS Re A ˆ 1 ( M ) Im A ˆ 1 ( M ) I ˆ ( P ) 1 W ( P) F Re A ˆ ( M ) F -1 F 2 F F Re[ A ( P )] Re[ P ( P )] Re[ iϕ ( ) -1 e iϕ Pˆ M e ] Re A ˆ 2 ( M ) Im A ˆ 2 ( M ) I ˆ ( P ) 2 ~ Re P ( P ) Arg W ( P ) Im A ˆ ( M ) Im[ A ( P )] Im[ P ( P )] e iϕ Im [ Pˆ ( M ) ] ~ Im P ( P ) Reconstructed WFE Image mask Lyot stop Re A ˆ 3 ( M ) Im A ˆ 3 ( M ) I ˆ ( P ) 3 Phase-shift algorithm Complex amplitude in image Complex amplitude in pupil Coronagraphic Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

11 Phase-shifting coronagraph Measured intensities 3 sequential phase-shifts φm = 0, 2π/3 and 4π/3 Behind Roddier phase mask Behind 4-quadeants phase mask Behind Vortex phase mask - Phase-shifting in pupil - Sensing in image - Phase-shifting in image - Sensing in pupil Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

12 Numerical results Measurement accuracy is fairly similar for all cases Low spatial frequency WFE: ypically in the range 5-10 % well below λ/100 RMS Mid spatial frequency is slightly worse: % As good as when there is no phase mask, except for the four-quadrant Initial WFE PV λ RMS λ ype of Coronagraph No coronagrah Roddier 4-Quadrants Vortex (m=2) PHASE-SHIF LOCAION elescope pupil Lyot stop Image ρ = 0.05; Λ = 4; 0.1 < η < 0.9 ρ = 0.05; Λ = 4; 0.1 < η < 0.9 ε = 0.1 (*) ; Λ = 4; 0 < η < 0.95 Measured (waves) Difference (waves) Relative error (%) Measured (waves) Difference (waves) Relative error (%) Measured (waves) Difference (waves) Relative error (%) RMS PV RMS PV RMS PV RMS PV Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

13 Numerical results Effect of Lyot stop Measurement accuracy is degraded by the Lyot stop WFE cannot be reconstructed if the diameters D and D L of the telescope pupil and Lyot stop are equal Best measurement accuracy achieved when D L / D 3 Relative errors (%) D DL/D L ratio Phase-shift in Lyot stop Phase-shift in coronagraph RMS PV RMS PV Negative Fail Fail Relative error (%) Phase-shifting in pupil PV RMS Phase-shifting in image PV RMS diameters ratio D L /D Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

14 Conclusion Phase-shifting techniques enable wavefront sensing behind the phase mask of a coronagraph Potential reduction of Non common path aberration (NCPA) Phase-shifting can be implemented either in pupil or in image. In both cases measurement accuracy is well below λ/100 RMS his type of WFS is not limited to weak aberration, but only by 2π-ambiguity It not limited to low order spatial frequency (low order Zernike modes) and could operate in open loop heir performance is degraded when operating behind the Lyot stop Optical solutions to be investigated: Independent optical arm? Dichroic Lyot stop? Integral field spectrograph? Conf echniques and Instrumentation for Detection of Exots VIII San Diego,

15 Phase-shifting coronagraph is good! Questions? Conf echniques and Instrumentation for Detection of Exots VIII San Diego,